What Is Your Sedimentation Rate?

Medically Reviewed by Kumar Shital, DO on September 18, 2023
4 min read

The sedimentation rate -- or “sed rate,” for short -- is a blood test that checks for inflammation in your body. It’s one clue for your doctor that you might have a disease linked to inflammation, like arthritis or cancer, or an infection.

The sed rate test measures how fast red blood cells fall to the bottom of a tube. Inflammation creates proteins that make red blood cells fall more quickly.

Another name for this test is erythrocyte sedimentation rate (ESR). Red blood cells are called erythrocytes. Sedimentation is the process by which they fall to the bottom of the tube.

Your doctor might order the sed rate test if you have symptoms like these:

The sed rate test can be part of the process of discovering if you have one of these conditions:

You might also get this test once you've started treatment for one of these conditions. The sed rate can help your doctor see how well your body is responding to treatment.

You don’t need to do anything special to prepare. It's just a basic blood test.

Let your doctor know what medicines (and supplements) you take before you have the test. Certain drugs can affect the results. Also let your doctor know if you are pregnant or are having your period.

A nurse or other health care provider will take a sample of your blood, usually from a vein in your arm. They will first tie a band around the upper part of your arm to make your vein fill with blood and swell up. Then they’ll clean the area with an antiseptic, and place a needle into your vein. Your blood will collect into a vial or tube.

The process should only take a couple of minutes. Afterward, you’ll get a piece of gauze and a bandage over the area to stop the bleeding.

You may feel a slight sting as your blood is drawn. Afterward, you may have a small bruise. You might feel dizzy and sore, and there might be some bleeding.

Your sample will go to a lab. You should have the results in 1 or 2 hours.

A lab technician will place your red blood cells into a tall, thin tube and check how far they fall in 1 hour. When you have inflammation in your body, abnormal proteins in your blood make red blood cells form into clumps. These clumps are heavy, so they fall to the bottom of the tube more quickly than single blood cells.

The faster the blood cells sink, the more inflammation you have in your body.

The sed rate test reports in millimeters (mm) the distance between the clear liquid (plasma) at the top of the tube and your red blood cells after 1 hour. The normal range is:

  • 0 to 15 mm/hour in men younger than 50
  • 0 to 20 mm/hour in men older than 50
  • 0 to 20 mm/hour in women younger than 50
  • 0 to 30 mm/hour for women older than 50
  • 0 to 10 mm/hour for a child

A high sed rate is a sign you may have a disease that causes inflammation in your body.

Some conditions and medicines can affect the speed at which red blood cells fall, and they may affect your test results. These include:

The sed rate test can only tell your doctor that you have inflammation somewhere in your body. It can't show where the inflammation is or what caused it. Your doctor may also test for your erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP) to help make a diagnosis. Both are acute phase reactants or inflammatory markers that can help point to a diagnosis or help follow treatment in a diagnosis. You will still need imaging or even biopsies to make a specific diagnosis.

Talk to your doctor about the results of your sed rate test, and any other tests you have. Make sure you understand what the results mean, and how they'll affect your treatment.